<h2>DESCRIPTION</h2>

<em>v.to.db</em> loads vector map features or metrics into a database
table, or prints them (or the SQL queries used to obtain them) in a
form of a human-readable report. For uploaded/printed category values
'-1' is used for 'no category' and 'null'/'-' if category cannot be
found or multiple categories were found. For line azimuths '-1' is used
for closed lines (start equals end).

<h2>NOTES</h2>
Measures of lengths and areas are always reported in meters, unless the
<em>unit</em> parameter is set.
The units <em>miles</em>, <em>feet</em>, <em>meters</em> and
<em>kilometers</em> are square for <em>option=area</em>.
<p>Feet and acre units are always reported in their common versions
(i.e. the International Foot, exactly 5280 feet in a mile), even
when the location's standard map unit is the US Survey foot.
<p>When calculating perimeters in Latitude-Longitude locations, the geodesic
distance between the vertices is used.
<p>When using <em>option=coor</em> on a vector area map, 
only coordinates of centroids with unique category will be reported.
<p>When using <em>option=bbox</em> on a vector area map with more than one
feature per category value, the results corresponds to the bounding box of 
all features of same category taken together.
<p>Line azimuth is calculated as angle from the North direction to the line endnode
direction at the line statnode. By default it's reported in decimal degrees (0-360, CW) but
it also may be repored in radians with <em>unit=radians</em>. Azimuth value
<b>-1</b> is used to report closed line with it's startnode and endnode being in
same place. Azimuth values make sense only if every vector line has only one
entry in database (unique CAT value).
<p>If the module is apparently slow <em>and</em> the map attributes are
stored in an external DBMS such as PostgreSQL, it is highly recommended
to create an index on the key (category) column.
<p>Uploading the vector map attributes to a database requires a table attached to
a given input vector <em>layer</em>. The <b>print only</b> (<b>-p</b>) mode
doesn't require a table. Use <em><a href="db.execute.html">db.execute</a></em>
or <em><a href="v.db.addtable.html">v.db.addtable</a></em> to create a table if
needed.
<p>Updating the table has to be done column-wise. The <em>column</em> will be
created in the table if it doesn't already exist, except when using the
<b>print only</b> (<b>-p</b>) mode. If the <em>column</em> exists, the
<b>--overwrite</b> flag is required to overwrite it.

<h2>EXAMPLES</h2>

<h3>Updating attribute tables</h3>

Upload category numbers to attribute table (used for new map):<br>
<div class="code"><pre>
v.to.db map=soils type=centroid option=cat
</pre></div>

<p>Upload polygon areas to corresponding centroid record in the attribute table:<br>
<div class="code"><pre>
v.to.db map=soils type=centroid option=area columns=area_size unit=h
</pre></div>

<p>Upload line lengths (in meters) of each vector line to attribute table
(use <em>v.category</em> in case of missing categories):<br>
<div class="code"><pre>
v.to.db map=roads option=length type=line columns=linelength units=me
</pre></div>

<p>Upload x and y coordinates from vector geometry to attribute table:<br>
<div class="code"><pre>
v.to.db map=pointsmap option=coor columns=x,y
</pre></div>

<p>Upload x, y and z coordinates from vector geometry to attribute table:<br>
<div class="code"><pre>
v.to.db map=pointsmap option=coor columns=x,y,z
</pre></div>

<p>Transfer attributes from a character column (with numeric contents) to a new
integer column:<br>
<div class="code"><pre>
v.db.addcolumn usa_income_employment2002 col="FIPS_NUM integer"
v.to.db usa_income_employment2002 option=query columns=FIPS_NUM query_column=STATE_FIPS
</pre></div>

<p>Upload category numbers of left and right area, to an attribute table of
boundaries common for the areas:<br>
<div class="code"><pre>
# add categories for boundaries of the input vector map, in layer 2:
v.category soils out=mysoils layer=2 type=boundary option=add
# add a table with columns named "left" and "right" to layer 2 of the input
# vector map:
v.db.addtable mysoils layer=2 columns="left integer,right integer"
# upload categories of left and right areas:
v.to.db mysoils option=sides columns=left,right layer=2
# display the result:
v.db.select mysoils layer=2
</pre></div>

<p>Compute D<sub>L</sub>, the Fractal Dimension (Mandelbrot, 1982), of the
boundary defining a polygon based on the formula:
<br><tt>
D = 2 * (log perimeter) / (log area):<br>
</tt>
<div class="code"><pre>
g.copy vect=soils,mysoils
v.db.addcolumn mysoils col="d double precision"
v.to.db mysoils option=fd column="d"

g.region vector=mysoils res=50
v.to.rast input=mysoils output=soils_fd type=area use=attr attribute_column=d
r.colors map=soils_fd color=gyr

d.mon wx0
d.rast.leg soils_fd
d.vect mysoils type=boundary
</pre></div>

<h3>Printing reports</h3>

Report x,y,z coordinates of points in the input vector map:<br>
<div class="code"><pre>
v.to.db -p bugsites option=coor type=point
</pre></div>

Report all area sizes of the input vector map:<br>
<div class="code"><pre>
v.to.db -p soils option=area type=boundary units=h
</pre></div>

<p>Report all area sizes of the input vector map, in hectares, sorted by category
number (requires GNU <em>sort</em> utility installed):<br>
<div class="code"><pre>
v.to.db -p soils option=area type=boundary units=h | sort -n
</pre></div>

<p>Report all line lengths of the input vector map, in kilometers:<br>
<div class="code"><pre>
v.to.db -p roads option=length type=line units=k
</pre></div>

<p>Report number of features for each category in the input vector map:<br>
<div class="code"><pre>
v.to.db -p roads option=count type=line
</pre></div>


<h2>SEE ALSO</h2>

<em>
<a href="d.what.vect.html">d.what.vect</a>,
<a href="db.execute.html">db.execute</a>,
<a href="v.category.html">v.category</a>,
<a href="v.db.addtable.html">v.db.addtable</a>,
<a href="v.db.addcolumn.html">v.db.addcolumn</a>,
<a href="v.db.connect.html">v.db.connect</a>,
<a href="v.distance.html">v.distance</a>,
<a href="v.report.html">v.report</a>,
<a href="v.univar.html">v.univar</a>,
<a href="v.what.html">v.what</a>
</em>


<h2>REFERENCES</h2>

<ul>
  <li>Mandelbrot, B. B. (1982). The fractal geometry of nature. New York: W. H. Freeman.</li>
  <li>Xu, Y. F. &amp; Sun, D. A. (2005). Geotechnique 55, No. 9, 691-695</li>
</ul>


<h2>AUTHOR</h2>

Radim Blazek, ITC-irst, Trento, Italy<br>
Line sinuousity implemented by Wolf Bergenheim

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